Pixel precise object picking

[GarbagePillow]

Hey guys.

Sometimes I want to be able to select an object using the mouse. Maybe there is some trick to doing this that is not obvious to me, but I have come up with a solution in this demo that seems to work. To do this I have a canvas that contains ID information, and a 1 pixel canvas for retrieving an ID.

Let me know what you think.

EJBve.png (147.69 KiB) Viewed 585 times

edit* ack, I meant to post this in the Projects and Demos forum, maybe its not appropriate here

[Xgoff]

i would think you could simply just do a getPixel() on an imagedata and check if a fully transparent pixel is under the mouse. you wouldn't need shaders or canvases for it either

[GarbagePillow]

i would think you could simply just do a getPixel() on an imagedata and check if a fully transparent pixel is under the mouse. you wouldn't need shaders or canvases for it either

Hmm... where does the imagedata come from?

[Xgoff]

i would think you could simply just do a getPixel() on an imagedata and check if a fully transparent pixel is under the mouse. you wouldn't need shaders or canvases for it either

Hmm... where does the imagedata come from?

love.image.newImageData

[Nixola]

You'd have to take a screenshot (an imagedata) to be sure the mouse is overlapping the object

[Xgoff]

You'd have to take a screenshot (an imagedata) to be sure the mouse is overlapping the object

not really, as long as the mouse pointer is within the bounding box of the image you can check it

[Nixola]

I was going to say that there's an easier/faster way... Then I tried to think and I stopped.
That means you're right; anyway, are you able to read this without quoting?

[GarbagePillow]

You'd have to take a screenshot (an imagedata) to be sure the mouse is overlapping the object

not really, as long as the mouse pointer is within the bounding box of the image you can check it

Ahh. I see what you are saying. Two points though: You would have to traverse through all the images overlapping the point you are checking until you hit one that did not have a transparent pixel at the location. Also, you would need to have imagedata for each image you loaded. This could easily take more space than maintaining an extra canvas.

[Xgoff]

You'd have to take a screenshot (an imagedata) to be sure the mouse is overlapping the object

not really, as long as the mouse pointer is within the bounding box of the image you can check it

Ahh. I see what you are saying. Two points though: You would have to traverse through all the images overlapping the point you are checking until you hit one that did not have a transparent pixel at the location. Also, you would need to have imagedata for each image you loaded. This could easily take more space than maintaining an extra canvas.

yes, that's a drawback. however, you'd probably need to implement it anyway as a fallback since not everybody's hardware can use canvases, and apparently some can't use shaders either

[Ref]

Hmm... where does the imagedata come from?

image_data = love.image.newImageData( "images/"..file )
img = G.newImage( image_data )